1. Field of the Invention
The invention relates generally to management of power allocation to storage devices, and more particularly, to management of power allocation to storage devices coupled with a controller through an expander.
2. Related Patents
This patent is related to commonly owned U.S. patent Ser. No. 12/510,699 entitled METHODS AND APPARATUS FOR POWER ALLOCATION IN A STORAGE SYSTEM, which is hereby incorporated by reference.
3. Discussion of Related Art
In a variety of electronic systems, a shared power source is used to power a number of devices of the system under control of a common control unit. For example, a storage system may coordinate the application of power from a power supply to each of a plurality of storage devices. In particular, each of the storage devices may be, for example, a rotating disk drive. Such devices may utilize minimal power when initially applied but may then consume substantially more power as the disk drive's motor starts to spin the rotating storage media within the disk drive. Although the disk drive may consume less power once the motor has reached the desired rotational speed (i.e., in steady state operation), initially the disk drive may require substantially more power to commence rotation and complete its initialization.
In many present-day storage systems including, for example, a Serial Attached SCSI (SAS) system, a controlling device (e.g., SAS initiator) coupled with the storage devices (e.g., SAS targets) may utilize command structures and protocol primitives/sequences to control and sequence the “spin-up” of each storage device under its control. The controlling device may limit the number of disk drives enabled to spin-up at any given point in time until eventually all disk drives are started and spinning. Thus, a controlling device may limit the spin-up power requirements for the disk drives under its control. However, the controlling device may not have knowledge of how long the disk drives may require the additional power to complete initialization. Thus, present controlling devices presume a worst-case scenario allowing a maximum possible time duration for the initialization of each disk drive coupled thereto. This solution may cause a significant, unnecessary delay in the initialization of the storage system and hence delays in access to the storage system by attached host systems.
In some storage system environments, the storage devices may be coupled to multiple controlling devices or may autonomously change their power consumptions status. Further, the controlling device may not even be coupled in the same power domain to allow it to have knowledge of the available power status of the storage devices.
Thus, it is an ongoing challenge to manage the power allocation for storage devices when the storage devices require additional power during initialization.